Monolithic array for solid state ultraviolet light emitters

ABSTRACT

The present invention is directed towards a source of ultraviolet energy, wherein the source is a UV-emitting LED&#39;s. In an embodiment of the invention, the UV-LED&#39;s are characterized by a base layer material including a substrate, a p-doped semiconductor material, a multiple quantum well, a n-doped semiconductor material, upon which base material a p-type metal resides and wherein the base structure has a mesa configuration, which mesa configuration may be rounded on a boundary surface, or which may be non-rounded, such as a mesa having an upper boundary surface that is flat. In other words, the p-type metal resides upon a mesa formed out of the base structure materials. In a more specific embodiment, the UV-LED structure includes n-type metallization layer, passivation layers, and bond pads positioned at appropriate locations of the device. In a more specific embodiment, the p-type metal layer is encapsulated in the encapsulating layer.

FIELD OF INVENTION

The present invention is directed to an LED, and arrays of same. Inparticular, the LED emits energy in the ultra-violet (optical wavelengthgreater than or equal to 150 nm and less than or equal to 410 nm)portion of the electromagnetic spectrum.

BACKGROUND OF THE INVENTION

Consideration has been given to using single color LED's, such as red,blue or green LED's, in combination with fluorescent and phosphorescentmaterials to produce another desired color. While certain materialsrespond fluorescently or phosphorescently to light from the visibleportion of the spectrum, and thus would respond to visible LED's, thereare a number of materials which respond to the relatively higher-energyphotons emitted in the ultraviolet portion of the spectrum. Furthermore,UV-emitting LED's may, in combination with the appropriate phosphor,prove to be a source of white light providing a high level ofsatisfaction. That is, white light generated from a UV LED andaccompanying phosphor may lack the artifacts of a colored light sourceemployed to produce light from an LED emitting in the colored portion ofthe visible spectrum. For example, this phenomenon is believed to affectblue LED's when used to excite a phosphor during production of whitelight, where the generated white light is believed to exhibit a bluecomponent. Accordingly, recent interest has focused upon the use of aUV-emitting LED.

At least certain prior art LED devices emit light in directions that maybe undesirable, such as through the sides of the diode, as opposed toonly substantially through the preferred side for the emission ofenergy. Depending upon the end use for which the LED is employed, thismay not be a problem. However, as indicated, there may be instanceswhere emissions in undesired directions have substantial unwantedconsequence. For example, in UV-induced fluorescence detectionapplications, stray UV light can dramatically increase the backgroundnoise in the photodetection of fluorescent light. Further, in suchapplication, it is preferred that a focused beam of UV light is providedto generate sufficient fluorescence for localized photodetection. At thevery least, emissions in undesired directions may be indicative of aninefficient device.

SUMMARY OF THE INVENTION

The present invention is directed towards a source of ultravioletenergy, wherein the source is a UV-emitting LED's. In an embodiment ofthe invention, the UV-LED's are characterized by a base layer materialincluding a substrate, a n-doped semiconductor material, a multiplequantum well, a p-doped semiconductor material, and corresponding n- andp-metallization in contact with the n- and p-layers respectively. Thebase layer material has a mesa configuration that may be rounded on aboundary surface, or which may be non-rounded, such as a mesa having anupper boundary surface that is flat. In other words, the p-type metalresides upon a mesa formed out of the base structure materials. In amore specific embodiment, the UV-LED structure includes passivationlayers and bond pads positioned at appropriate locations of the device.In a more specific embodiment, the p-type metal layer is encapsulated inthe encapsulating layer.

In yet another embodiment, LED's substantially as described above, arearranged spatially and/or arrayed in particular arrangements that vary,for example, the number of rows of diodes, the number of diodes per row,diode spacing, the amount of n-metal present between each mesa, anddiode offsets—that is, the offset between diodes of a given row and thediodes of an adjacent row, as indicated later in this paper. In yetanother embodiment, circular diodes of specified diameters are employed.In one specific embodiment, the diode diameters are about 100 μm or evenless. Such arrangements and combinations thereof, have been found toimprove the output of UV energy, for example, by improving currentspreading through the LED's. Furthermore, the arrangement andcombinations provide the artisan with the ability to adjust the outputfrom the device and/or minimize, if not eliminate, undesired effectsthat result where unwanted material defects enter the field of emission,which would otherwise interfere with the emission of light.

It is believed that the structures described herein are capable oftransmitting a collimated band of energy, which is desirable for devicesin which narrow transmission bands are desired. For example, a device ofthe present invention, emitting collimated energy, may be employed in adevice detecting the presence or absence of a given thing, and/or forthe measurement of same, where for instance, the presence, absence, ormeasurement of that phenomena is in some way related to the measurementof the emission after it encounters (or does not encounter) the thing tobe detected or measured. In these instances, generalized emissions (suchas through the side of the device), could render the measurement lessaccurate or reliable.

Also, it is believed that output from the diodes of the presentinvention are substantially limited to the UV-portion of theelectromagnetic spectrum. In other words, the output is substantiallydevoid of emissions in the visible portion of the spectrum, such asvisible light in the yellow portion of the spectrum. This may be due toimproved current spreading which allows higher current densities and“swamping out” of defect emission by near-band-edge emission. However,having smaller mesas, less than 100 um in diameter, also reduces theoptical volume of n- and p-cladding layers, which may be plagued withsub-band-edge luminescent structural and point defects, allowing lightto escape the mesa in a shorter optical path length.

In another aspect of the present invention, LEDs of the presentinvention are arrayed in linear, triple, and compact arrays, asdescribed herein. In a more specific embodiment of the invention, theLEDs are circular in shape, having diameters not exceeding 100 μm, andare spaced by a predetermined amount of n-metallization layer, asmeasured linearly, between adjacent diodes.

In another aspect of the invention, the LED's of the present inventionhave mesas that are provided with a rounded boundary surface contourresembling, for example, a hemisphere or parabola, an ellipse, orcombinations thereof.

In one aspect, the term “collimated” light or energy refers to aparallel or substantially parallel band of energy emitted from its diodesource, with lateral energy spreading, away from the cross-sectionalarea of the diode, limited to approximately +/−15° as measured radiallyfrom a line extending from the edge of the emission source, in thedirection of the emitted energy.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a LED of the present invention, depicted in cross-section;

FIG. 1 a is a top plan view of the LED of the present invention;

FIG. 2 depicts the formation of a LED of the present invention, incross-section, at a relatively early stage of production;

FIG. 2 a is atop plan view of the LED depicted in FIG. 2;

FIG. 3 depicts the formation of a LED of the present invention, incross-section, subsequent to the FIG. 2 depiction;

FIG. 3 a is a top plan view of the LED depicted in FIG. 3;

FIG. 4 depicts the formation of a LED of the present invention, incross-section, subsequent to the FIG. 3 depiction;

FIG. 4 a is a top plan view of the LED depicted in FIG. 4;

FIG. 5 depicts the formation of a LED of the present invention, incross-section, subsequent to the FIG. 4 depiction;

FIG. 5 a is a top plan view of the LED shown in FIG. 5 depiction;

FIG. 6 depicts the formation of a LED of the present invention, incross-section, subsequent to the FIG. 5 depiction;

FIG. 6 a is a top plan view of the LED shown in FIG. 6;

FIG. 7 depicts the formation of a LED of the present invention incross-section, subsequent to the FIG. 6 depiction;

FIG. 7 a is a top plan view of the LED shown in FIG. 7;

FIG. 8 is a cross-sectional view of a substrate employed in the LED ofthe present invention;

FIG. 9 is a cross sectional view of a circular LED of the presentinvention;

FIG. 10 is a cross sectional view of adjacent LED's (and the regionbetween them);

FIG. 11 is a top plan view of 25 μm circular diodes;

FIG. 12 is a top plan view of 50 μm circular diodes;

FIG. 13 is a top plan view of 100 μm circular diodes;

FIG. 14 is a top plan view of 25 μm circular diodes in an offset lineararray;

FIG. 15 is a top plan view of a compact array;

FIG. 16 is a top plan view of a triple array;

FIG. 17 is a top plan view of a single linear array;

FIG. 18 is a top plan view depicting a particular arrangement;

FIG. 19 is a cross sectioned view of an embodiment of the presentinvention;

FIG. 20 is a cross sectional view of an embodiment of the presentinvention;

FIG. 21 is a cross sectional view depicting collimation in the LED'sshown in FIG. 20.

FIG. 22 is a cross sectional view of an embodiment of the presentinvention.

FIG. 22 a is a cross sectional view of the embodiment shown in FIG. 22.

FIG. 23 is a cross sectional view showing the parabolic mirror effect oflight leaving the mesa of the structure shown in FIG. 24.

FIG. 24 is a cross sectional view of a particular arrangement of LEDs ofthe type shown in FIG. 22.

DETAILED DESCRIPTION OF THE INVENTION

An LED 10 of the present invention is depicted in FIG. 1. It should beunderstood that the LED will be incorporated into arrays including aplurality of LED's, which is discussed and shown later in thisdisclosure.

LED 10 includes the following components: base layer 12, p-metal layer14, encapsulant 16, mesa 18, n-metallization layer 20, passivation layer22, p-bond pad 24 and n-bond pad 26 (not shown in FIG. 1). The bond padsare used to connect the device to a suitable package.

Base layer 12 is a multiple component element. As depicted in FIG. 8,base layer 12 includes a substrate 30, such as a substrate of sapphire,silicon carbide, zinc oxide, gallium nitride, and any combination of agallium nitride-aluminum-indium alloy of the formulaAl_(x)In_(y)Ga_(l-x-y)N, wherein x+y<1, and GaAF. An epitaxial layer ofan n-doped containing material 32 is deposited upon the substrate 30.Here the n-doped material may be any conventional material, such as GaNdoped with silicon. As shown in FIG. 8, a silicon dopant is present inone or more delta doped layers, that is, one or more discreet layers 34of dopant. A delta-doped arrangement may be advantageous in terms ofpromoting structural integrity of the device and/or facilitatingspreading of current through the base structure. However, other dopingschemes may be employed instead of delta doping. An active region ofmultiple quantum wells (MQW's) 36 is positioned upon the n-claddinglayer. MQW's may be constructed of material known to be suited for thispurpose, such as alternating layers of undoped aluminum indium galliumnitride alloys, doped or undoped, of any stoichiometry, having differentratios of aluminum, indium, and gallium for quantum confinement. A layerof p-doped material 38, such as GaN, AlGaN, or AlInGaN (anystoichiometry) doped with Mg, is deposited upon the MQW layer.

Group III-nitride epitaxial films are typically deposited using MOCVD(metal organic chemical vapor deposition), MBE (molecular beam epitaxy),HVPE (hydride vapor phase epitaxy) or other epitaxial depositiontechnique. The substrate can be any variety of materials: sapphire,silicon, SiC, GaN, AlN, InN, AlIn, AlInGaN with any alloy combination,lithium gallate, etc.

Before epitaxy, the precleaned wafers are annealed at high temperaturein hydrogen and subsequently in ammonia. An optional template layer fornucleation, followed by a III-nitride template layer, are thendeposited. A cladding layer is then deposited (typically n-cladding)followed by an active region (typically a multiple quantum well) ablocking layer (typically undoped) and another cladding layer (typicallyp-doped). The cladding layers are either uniformly doped, delta-doped,or grown as doped superlattices. N-type doping usually involves Siincorporation whereas p-type doping usually involves Mg incorporation.

Fabrication usually begins with a surface cleaning using solvents (fordegreasing) and acids (for metal and oxide removal). Patterning of allmask levels is readily done with standard photoresist-basedmicrofabrication techniques. The p-contact metallization (typically Ni,Pt, Ag, or Ni/Au) is typically defined first using e-beam evaporation orsputtering. P-contact encapsulation (via selective sputtering of TiW,for example) is preferred to prevent p-contact segregation at hightemperature anneals and at high forward bias over time. Placing TiWbetween the n-contact metallization and n-bond metallization has alsobeen found to help encapsulate the n-contact and prevent alloyingbetween contact and bond metallization. If a rounded (i.e., parabolic,elliptical, spherical) mesa is fabricated, then it may be so done usingreactive ion etching (RIE) and inductively coupled plasma (ICP) etchingor etching with a chlorine-based chemistry by reflowing resist viaelevated heating over time, by grading the photomask in absence ofreflow, or by combining both. It should be kept in mind that thechemistry of the resist is quite important for controlling the mesasidewall geometry. For example, AZ1512 positive resist for sidewallformation has been used successfully. N-contact metallization (typicallyTi/Al) is then deposited using e-beam evaporation or sputtering,followed by passivation (typically sputtered SiO₂) and bond metaldeposition (typically Ni/Au).

Devices may be packaged using GE COB (Chip On Board) flip-chiptechnology to avoid a silicon submount. In this case, the chip ismounted directly to a PCB board with solder bumps.

Turning now to FIGS. 2-7, and then back to FIG. 1, a process forfabricating LED's of the present invention and arrays of same, shall bedescribed. FIG. 2 depicts a p-metal layer 14 deposited over the baselayer 12. P-metal layer may be selected from nickel, rhodium, silver,aluminum, palladium or alloys of same, alloys of Ni—Au, NiO—Au, NiO—Ag,indium-tin-oxide alloys and silver oxide, to enumerate just a fewsuitable materials. The p-metal can be a non-transparent, reflective orsemi-reflective material, such as NiAu, in which case the lightgenerated by the diodes is reflected by the p-pad metal and exits theback of the device. However, arrangements wherein the p-metalmetallization is transparent, allowing light to exit the top of thedevice, are acceptable. A transparent p-metallization can be constructedof thin layers of nickel, platinum, silver, alloys of NiO—Au, NiO—Ag,alloys of In—Sn—O, AgO, rhodium, palladium or platinum.

FIG. 3 depicts the device after the p-metal 14 layer has been formedinto circular diodes. It should be noted that other diode shapes mightbe employed, depending upon the intended usage of the completedstructure; however, a circular geometry is desired for maximal currentspreading. The p-metal may be formed by applying a photoresist layer(either positive or negative photoresist) that has been patterned uponthe p-metal layer, with openings provided in the photoresist tocorrespond to locations where p-metal is to be removed. After developingthe resist, the device is subjected to a wet etch in order to remove thep-metal at derived locations. Subsequent to etching, the photoresist isremoved from the device. While one diode is shown in FIG. 3, it will beappreciated that in many instances a plurality of diodes will be formedthe base layer 12, in accordance with the desired diode diameter,pattern, and spacing of same as described later in this disclosure.

The p-metal can be patterned by dry etching techniques, such as RIE andICP etching. As shown in FIG. 3 a, the p-metal has been patterned into acircular shape, while other shapes can be employed, circular diodes arewell suited to the production of a source of collimated light.

FIG. 4 depicts the device after an encapsulant 16 has been applied overand encapsulates the p-metal layer. The encapsulating layer may beapplied by standard photolithographic techniques employing a positive ornegative photoresist patterned into a mask, development of the mask,application of the encapsulating material, and removal of the mask. ATi—W alloy may be employed as the material for the encapsulating layer.Because TiW cannot be easily selectively wet-etched,reactive-ion-etching and/or resist liftoff are preferred for selectivelypatterning TiW encapsulation over the p-contact metallization.

FIG. 5 shows device 10 after formation of the mesa 18. As shown, mesa 18is formed where a preselected portion of base layer 12 is removed fromaround the p-metal layer 14. Mesas can be formed by patterning a resist(either positive or negative) upon the device, developing the resist inpre-selected areas, selective removal of undeveloped or developed resistand subsequently etching (via wet or dry techniques), portions ofsubstrate selected for removal. ICP etching or RIE etching have beenfound to be well suited for this process step. Though the dry etchprocess also removes layers of the resist mask as well as the GaN alloy,the thickness of the resist mask prevents complete removal during dryetching, which usually consists of a chlorine-based chemistry. Theremaining resist mask is subsequently chemically stripped from thesurface.

As shown in FIG. 8, when forming the mesa in the substrate 30, a portionof the n-doped containing material, active region 36, and p-dopedcontaining material 38 have been removed. However, other arrangementsare possible, where only a portion of p-doped material 38 and/or activeregion 36 are removed during mesa formation. Also, it should be notedthat the arrangements other than shown in FIG. 8 are possible, whereinfor example, the location of the n-doped layer and p-doped layer arereversed, and/or additional doped or undoped layers are present.

FIG. 6 depicts the device after n-metal layer 20, such as titanium,aluminum, titanium-aluminum alloy, titanium tungsten aluminum alloy,TiW, tantalum alloy, or tantalum has been deposited upon the device. Aresist is applied to the device, developed at selected locations,removed at undeveloped or developed locations (depending on the use ofnegative or positive resist), and the n-metal is deposited in thedesired areas. The resist is then removed from the device.

The n-metal layer is deposited so as to enclose the p-metal layer andmesa within a boundary of n-metal layer, as depicted in FIG. 6 a. Sizingof the p-metal layer, and spacing from the p-metal layer and mesa edge,will be discussed later in this disclosure.

As shown in FIG. 6, the n-metal layer has been deposited on the sameside of the base layer on which the p-metal has been deposited. Thisarrangement is employed where a non-conductive material, such assapphire, is employed as substrate 30. Where the base layer is anelectrically conductive material, such as the silicon carbide, orAl_(x)In_(y)G_(a1-x-y)N alloys discussed previously, the n-contactlayers may be formed on the side of the substrate opposite the side onwhich the p-metal layer is positioned.

FIG. 7 depicts the device after formation of a passivation layer 22,which may be a layer of SiO₂, SiN, or any suitable oxide or nitride.Passivation layer 20 is positioned over the n-metal contact and extendsover the mesa edge to partially encapsulate the p-metal layer 14, withan opening in the passivation layer provided in the top in order toprovide electrical contact between p-bond pad and the p-metal layer. Thepassivation layer may be deposited in accordance with photolithographictechniques previously disclosed, with subsequent removal of the mask.

FIG. 1 shows the LED after the p-bond pad 24 has been formed to contactthe p-metal layer 14. If the p-metallization is chosen to be reflective,it is preferred that the p-bond metal not cover the entirep-metallization, so that area is open for light extraction from the topof the device. For example, the p-bond pad and or the p-metallizationmay be deposited in a grid type pattern to facilitate the transmissionof light through the bond pad. The p-bond pad may be applied inaccordance with conventional photolithographic techniques as describedherein, including wet etching or dry etching after application anddevelopment of a mask patterned from a photoresist. The p-bond padelectrically connects the diode to a package or to an electric source.The p-bond metal may consist of Ni & Au, with interlayers of TiW toprevent alloying and metal absorption during high temperature soldering.

As shown in FIG. 9, the applicants have learned that, where the diode iscircular and has a diameter of 25 μm, the passivation layer 22 shouldoverlap with the p-metal layer 14 for about 2 μm on the upper side ofthe p-metal layer. For diodes of larger diameters (e.g. 50 μm and 100μm), the passivation layer/p-metal layer overlap should be about 5 μm.

The applicants have further found that the linear distance occupied bythe n-metal layer, as measured laterally, between adjacent diodes (SeeFIG. 10), is dependent upon on diode diameter. For example, where anarray of about 25 μm diameter diodes are arranged in a linear array,about 10 μm of n-metal should be present (a linear array is what itsname implies, a number of diodes arranged in a single line). About 20 μmof n-doped metal should be present between arrays of about 25 μmcircular diodes in a triple, compact, or an offset linear array. SeeFIGS. 11 and 14. (A triple array is arrangement of three lines ofdiodes. The diodes of one line may be may be offset from the diodes ofthe other line. A compact array is an arrangement of four or more linesof diodes. The diodes of a given line may be offset from the diodes ofadjacent line or adjacent lines. An offset linear array is anarrangement of two lines of diodes. The diodes of a given line may beoffset from the diodes of adjacent line or adjacent lines.) For 50 μldiameter diodes in a linear array, about 10 μm of n-metal layer shouldbe present between adjacent diodes. See FIG. 12. 20 μm should be presentbetween 50 μm diodes arranged in a triple array or an offset lineararray, and about 25 μm of n-metal should be present between adjacent 50μm diodes arranged in a compact array. See FIG. 12. For 100 μm circulardiodes, about 20 μm of n-metal layer should be present between adjacentdiodes arrayed in a linear array, about 30 μm of n-metal should bepresent between adjacent diodes arranged in a triple array or an offsetlinear array, and about 35 μm of n-metal should be present betweenadjacent diodes arranged in a compact array (see FIG. 13). Theguidelines set forth above are summarized in Table 1 below. TABLE 1Array Type Linear Triple Compact  25 μm 10 20 20  50 μm 10 20 25 100 μm20 30 35

The applicants have found that, for compact arrays, a 10×10 arrangementis well suited for 25 μm diodes. For 50 μm and 100 μm diodes, thearrangements may be, respectively, 7×7 and 4×4.

The applicants have further found that the distance between the p-metallayer 14 and edge of the mesa 18 should be about 6 μm (see, e.g. FIGS. 9and 11), and that the distance between the n-metal layer 20 to the mesa18 should be about 6 μm. See, e.g. FIG. 10. Thus, about 12 μm should bepresent between the p-metal and the n-metal layer. This arrangement iswell suited for linear arrays, compact arrays, and triple arrays.

FIGS. 11 through 14 illustrate circular diodes arranged in linear arraysand in offset arrays. Linear arrays are effective at emitting energyover a concentrated area however, such area is relatively narrow.Arrangements such as compact arrays or offset arrays broaden the areaover which energy is emitted, however the emissions tend to be moreefficient (as a function of current applied to the diodes) where diodesare smaller and the number of rows of diodes are relatively few. Thus,it may be appreciated that the offset and/or triple array arrangementprovides a relatively fair balancing of two desirable attributes:providing a fairly broad area of coverage and a fair degree ofefficiency of energy output based on applied current. Further, as thedesired UV focal feature for particle detection is a narrow line widthgreater than or equal to a single particle diameter and smaller thantwice the diameter of a single particle, linear arrays allow for a densefocal line beam to be imaged with simple optics.

FIG. 15 demonstrates a compact array format arrayed upon a substratehaving approximate dimensions of about 1000 μm×600 μm. Suitable arrayformats are for 25 μm diodes, 10×10, for 50 μm diodes, 7×7, and 100 μmdiodes, 4×4. Approximate spacing between the positive bond pad 24 andnegative bond pad 26 in approximately 250 μm, as shown in FIG. 16. Thenegative bond pad is positioned on or within the substrate, and makeselectrical contact with the n-metal, which is formed upon the substratein a manner that permits it to contact the n-pad and complete thecircuit.

FIG. 16 shows an triple array arranged upon a substrate havingapproximate dimensions of about 600 μm×600 μm. Suitable array formatsare, for 25 μm diodes, 3×10, for 50 μm diodes, 3×7, and for 100 μmdiodes, 3×4. Spacing between the diodes is as indicated previously.Approximate spacing between the positive bond pad 24 and the negativebond pad is approximately 250 μm. Triple arrays, where the lines ofdiodes are offset, provide a firewall effect to decrease, if noteliminate, the possibility that a particle traveling through the fieldof emission will not encounter emitted UV-energy. Such an arrangement iswell suited to a detection system where the encounter between a particleand emitted energy will result in a measurable effect.

As shown in the figures, the diodes of adjacent rows are offset by thelength of one-half mesa. However, the diodes may be offset in otherarrangements, such as one-third to one-half mesa in length.

FIG. 17 shows a single linear array shown in a substrate havingapproximate dimensions of 600 μm×600 μm. Suitable arrangements are, for25 μm diameter diodes, 10 diodes, for 50 μm diodes, 7 diodes and for 100μm diodes: 4 diodes.

The applicants have learned that the p-bond pad metal 24 should bedistanced about 20 μm from the n-metallization metal. Also, the padmetal should cover the p-metal by about 20 μm from the edge of thep-metal. See FIG. 18.

FIG. 19 depicts a side view of a plurality of diodes, with thepassivation layer not shown. Here, the mesas resemble trapezoids withthe p-metal layer 14 situated at the peak and the n-metal situated inthe valleys. P- and n-bond metal may be on top of the p- andn-metallization.

FIG. 20 depicts a plurality of diodes wherein the sidewalls of the mesasare rounded. A rounded arrangement may be advantageous in terms ofcollimating the transmission of light, as shown in FIG. 21. That is,where the sidewalls of the mesas are rounded, substantially all light isemitted from the center of the diode. Rounded mesa sidewalls can beproduced by engaging in a reflo process prior to etching.

Mesa height should be approximately 500 Å to 20 μm, with about 7000 Åbeing well suited for producing collimated light.

As further shown in FIG. 22, for parabolic mesas, it has been found thata specific arrangement in which the distance between the edges of thep-contact and n-contact is greater than or equal to the edge-to-edgedistance (x), but preferably 2x, of the p-contact, yields collimatedlight.

Due to the high resistivity of the p-cladding layers, i.e.—sheetresistance typically greater than 10,000 ohms per square, the activeregion is defined largely by the size of the p-contact metallization.

As shown in FIG. 23, good results are obtained when the height of therounded region of the mesa is 0.5 to 5 μm. Also the edge-to-edgedistance of the mesa should be about 5 to 5000 μm.

1. A linear array of mesa LED's that emit UV energy, wherein the mesaLED's of the linear array are comprised of a substrate having: a baselayer; an active region; a p-doped region; a n-doped region; wherein thesubstrate is formed into a plurality of mesas; a p-metallization regionis positioned on the mesa; a n-metallization region spaced from thep-metallization layer; wherein the p-metallization layer andn-metallization layer are in contact with electrical contacts; whereinthe mesa LED's are arranged in a linear array.
 2. The linear array ofclaim 1 wherein the p-metallization layer is positioned within anencapsulated layer selected from Ti—W alloy, W, Co, Mo, Cr, and otherrefractory metals.
 3. The linear array of claim 1 wherein the LED isfurther comprised of a passivation layer encasing at least a portion ofa region including the p-metallization layer, mesa, and n-metallizationlayer.
 4. The linear array of claim 2 wherein the LED is furthercomprised of a passivation layer encasing at least a portion of a regionincluding the encapsulating layer, mesa, and n-metallization layer. 5.The linear array of claim 1 wherein the mesa is circular in shape andhas a diameter selected between 10 μm and 150 μm, with preferablediameters of 20-30 μm, 40-60 μm, or 80-120 μm.
 6. The linear array ofclaim 1 wherein the n-metallization layer and p-metallization layer arespaced by about 12 μm.
 7. The linear array of claim 1 wherein the LED'shave a circular diameter of about 25 μm and about 1 to about 50 μm,preferably about 10 μm, of n-metallization layer is present betweenneighboring LED's.
 8. The linear array of claim 1 wherein the LED's havea circular diameter of about 50 μm and about 1 to about 100 μm,preferably about 10 μm, of n-metallization layer is present betweenneighboring LED's.
 9. The linear array of claim 1 wherein the LED's havea circular diameter of about 100 μm and about 1 to about 200 μm,preferably about 20 μm, of n-metallization layer is present betweenneighboring LED's.
 10. The linear array of claim 1 wherein the mesastructure has a shape selected from the group consisting of spherical,elliptical, parabolic, or any combination of these shapes.
 11. A triplearray of mesa LED's that emit UV energy, wherein the mesa LED's of thetriple array are comprised of a substrate having: a base layer; anactive region; a p-doped region; a n-doped region; wherein the substrateis formed into a plurality of mesas; a p-metallization region ispositioned on the mesa; a n-metallization region is spaced from thep-metallization layer; wherein the p-metallization layer andn-metallization layer are in contact with electrical contacts; whereinthe mesa LED's are arranged in a triple array.
 12. The triple array ofclaim 11 wherein the p-metallization layer is positioned within anencapsulated layer selected from Ti—W alloy, W, Co, Mo, Cr, and otherrefractory metals.
 13. The triple array of claim 11 wherein the LED isfurther comprised of a passivation layer encasing at least a portion ofa region including the p-metallization layer, mesa, and n-metallizationlayer.
 14. The triple array of claim 12 wherein the LED is furthercomprised of a passivation layer encasing at least a portion of a regionincluding the encapsulating layer, mesa, and n-metallization layer. 15.The triple array of claim 11 wherein the LEDs have a circular diameterof about 25 μm and about 1 to about 50 μm, preferably about 20 μm, ofn-metallization is present between neighboring LED's.
 16. The triplearray of claim 11 wherein the LEDs have a circular diameter of about 50μm and about 1 to about 100 μm, preferably about 20 μm, ofn-metallization is present between neighboring LED's.
 17. The triplearray of claim 11 wherein the LEDs have a circular diameter of about 100μm and about 1 to about 200 μm, preferably about 30 μm, ofn-metallization is present between neighboring LED's.
 18. The triplearray of claim 11 wherein the mesa is circular in shape and has adiameter selected from 25 μm, 50 μm, and 100 μm.
 19. The triple array ofclaim 11 wherein the n-metallization layer and p-metallization layer arespaced by about 12 μm.
 20. The triple array of claim 11 wherein the mesastructure has a shape selected from the group consisting of spherical,elliptical, and parabolic, or any combination of these shapes.
 21. Acompact array of mesa LED's that emit UV energy, wherein the mesa LED'sof the compact array are comprised of a substrate having: a base layer;an active region; a p-doped region; a n-doped region; wherein thesubstrate is formed into a plurality of mesas; a p-metallization regionis positioned on the mesa; a n-metallization region is spaced from thep-metallization layer; wherein the p-metallization layer andn-metallization layer are in contact with electrical contacts; whereinthe mesa LED's are arranged in a compact array.
 22. The compact array ofclaim 21 wherein the p-metallization layer is positioned within anencapsulated layer selected from Ti—W alloy, W, Co, Mo, Cr, and otherrefractory metals.
 23. The compact array of claim 21 wherein the LED isfurther comprised of a passivation layer encasing at least a portion ofa region including the p-metallization layer, mesa, and n-metallizationlayer.
 24. The compact array of claim 22 wherein the LED is furthercomprised of a passivation layer encasing at least a portion of a regionincluding the encapsulating layer, mesa, and n-metallization layer. 25.The compact array of claim 21 wherein the LEDs have a circular diameterof about 25 μm and wherein about 1 to about 50 μm, preferably about 20μm, of n-metallization is present neighboring LED's.
 26. The compactarray of claim 21 wherein the LEDs have a circular diameter of about 50μm and wherein about 1 to about 100 μm, preferably about 25 μm, ofn-metallization is present neighboring LED's.
 27. The compact array ofclaim 21 wherein the LEDs have a circular diameter of about 100 μm andwherein about 1 to about 200 μm, preferably about 35 μm, ofn-metallization is present neighboring LED's.
 28. The compact array ofclaim 21 wherein the mesa is circular in shape and has a diameterselected from 25 μm, 50 μm, and 100 μm.
 29. The compact array of claim21 wherein the n-metallization layer and p-metallization layer arespaced by about 12 μm.
 30. The compact array of claim 21 wherein themesa structure has a shape selected from the group consisting ofspherical, elliptical, and parabolic, or any combination of theseshapes.
 31. An offset linear array of mesa LED's that emit UV energy,wherein the mesa LED's of the offset linear array are comprised of asubstrate having: a base layer; an active region; a p-doped region; an-doped region; wherein the substrate is formed into a plurality ofmesas; a p-metallization region is positioned on the mesa; an-metallization region is spaced from the p-metallization layer; whereinthe p-metallization layer and n-metallization layer are in contact withelectrical contacts; wherein the mesa LED's are arranged in an offsetlinear array.
 32. The offset linear array of claim 31 wherein thep-metallization layer is positioned within an encapsulated layerselected from Ti—W alloy, W, Co, Mo, Cr, and other refractory metals.33. The offset linear array of claim 31 wherein the LED is furthercomprised of a passivation layer encasing at least a portion of a regionincluding the p-metallization layer, mesa, and n-metallization layer.34. The offset linear array of claim 32 wherein the LED is furthercomprised of a passivation layer encasing at least a portion of a regionincluding the encapsulating layer, mesa, and n-metallization layer. 35.The offset linear array of claim 31 wherein the LEDs have a circulardiameter of about 25 μm and wherein 1 to about 50 μm, preferably about20 μm, of n-metallization is present between neighboring LED's.
 36. Theoffset linear array of claim 31 wherein the LEDs have a circulardiameter of about 50 μm and wherein 1 to about 100 μm, preferably about20 μm, of n-metallization is present between neighboring LED's.
 37. Theoffset linear array of claim 31 wherein the LEDs have a circulardiameter of about 100 μm and wherein 1 to about 200 μm, preferably about30 μm, of n-metallization is present between neighboring LED's.
 38. Theoffset linear array of claim 31 wherein the mesa is circular in shapeand has a diameter selected from 25 μm, 50 μm, and 100 μm.
 39. Theoffset linear array of claim 31 wherein the n-metallization layer andp-metallization layer are spaced by about 12 μm.
 40. The offset lineararray of claim 31 wherein the mesa structure has a shape selected fromthe group consisting of spherical, elliptical, and parabolic, or anycombination of these shapes.